Like D, all headache pills can stop your headache. But when you are in pain, you want relief right away. No headache pill stops pain more quickly.
E & J suffer from a headache. E takes D and J takes its competitor. What could be properly concluded?
The advertisement basically tells us that all the pills are effective at stopping the pain, but D is at least as fast-acting as the other brands or faster. Notice the ad never says it stops the pain more quickly than any other brands, just that "no [other] pill stops pain more quickly." Is it possible that other pills stop the pain equally as fast as D? Sure, that is what the wording of the ad suggests.
(C) correctly concludes that E headache will be relieved at least as fast (or possibly faster) than J.